1. Field of the Invention
The present invention relates to a recording medium discrimination apparatus and method, and more particularly to a recording medium discrimination apparatus and method for distinguishing between the types of a recording medium by detecting reflected light from a surface of the recording medium and the quantity of transmitted light through the recording medium.
2. Description of Related Art
An image forming apparatus such as a copying machine and laser printer transfers to a recording medium an image to be visualized and developed by a developing section, and fixes the developed image by applying heat and pressure in predetermined fixing conditions. Since the predetermined fixing conditions differ greatly depending on the material, thickness, surface processing and the like of the recording medium, meticulous settings in accordance with the types of the recording medium are required to make full use of a plurality of types of the recording medium.
Conventionally, such an image forming apparatus displays the sizes and types of the recording medium (paper type when the recording medium is paper) on the operating panel mounted on the image forming apparatus for a user to select, and changes the fixing conditions (such as fixing temperature and transport speed of the recording medium passing through the fixing apparatus) in response to the selection.
In contrast with such a manual method, a technique has been proposed recently which automatically discriminates between the types of the recording medium with a sensor installed in the image forming apparatus for differentiating the recording medium, and carries out variable control of the developing conditions, transfer conditions or fixing conditions in response to the type differentiated.
The technique for automatically detecting the type of the recording medium includes the following methods: a method of acquiring a surface image of the recording medium with a CCD sensor, and detecting the degree of the surface smoothness of the recording medium by converting the information to fractal dimension information; a method of acquiring a surface image of the recording medium with a CCD sensor or CMOS sensor, and discriminating between paper types from the degree of the surface smoothness by detecting the degree of the roughness of the recording medium from the intensity of the light of the surface image; and a method of detecting the thickness of the recording medium from the length of a shadow formed at the edge of the recording medium (for example, see Japanese patent application laid-open No. 2001-139189).
However, the foregoing methods of detecting the degree of the surface smoothness of the recording medium cannot discriminate between recording media such as plain paper and cardboard which have nearly the same surface smoothness, but have a different compression state of paper fibers. Thus, the method can make a wrong decision of the cardboard as plain paper, and hence cannot carry out suitable settings for the recording paper in terms of the developing conditions, fixing conditions and transfer conditions, thereby offering a problem of deteriorating the fixing property.
On the other hand, as for the method of deciding the thickness of the material of the recording medium, it cannot discern the smoothness of the surface of the recording medium. Thus, as to glossy paper or the like which has more difficulty in passing light than plain paper, it makes a thicker decision as to the thickness of the material, and hence prevents proper setting of the conditions.
In addition, in spite of increasing types of recording media, demands for print quality have been increased recently, and hence accurate discrimination between a wide variety of recording media is required.